Using a cascade flag to process a copy relationship having a backward cascade copy relationship

ABSTRACT

Provided are a computer program product, system, and method for using a cascade flag to process a copy relationship having a backward cascade copy relationship. Each of a plurality of copy relationships indicates to copy source data to target data and has a cascade flag. The cascade flag for a forward copy relationship of the copy relationships is set to a first value in response to determining that the source data for the forward copy relationship comprises target data for a backward copy relationship and that a background copy operation specified to copy source data to target data of the backward copy relationship has not completed. The cascade flag for the forward copy relationship is set to a second value in response to determining that the backward copy relationship does not have an uncompleted background copy operation.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a computer program product, system, andmethod for using a cascade flag to process a copy relationship having abackward cascade copy relationship.

2. Description of the Related Art

In a storage environment, a storage controller may create point-in-time(“PiT”) copies of a production volume using point-in-time copytechniques, such as the IBM FlashCopy® (FlashCopy is a registeredtrademark of IBM), snapshot, etc. A point-in-time copy replicates datain a manner that appears instantaneous and allows a host to continueaccessing the source volume while actual data transfers to the copyvolume are deferred to a later time. The point-in-time copy appearsinstantaneous because Input/Output (“I/O”) complete is returned to thecopy operation in response to generating the relationship datastructures without copying the data from the source to the targetvolumes. Point-in-time copy techniques typically defer the transfer ofthe data in the source volume at the time the point-in-time copyrelationship was established to the copy target volume until a writeoperation is requested to that data block on the source volume. Datatransfers may also proceed as a background copy process with minimalimpact on system performance. The point-in-time copy relationships thatare immediately established in response to the point-in-time copycommand include a bitmap or other data structure indicating the locationof blocks in the volume at either the source volume or the copy volume.The point-in-time copy comprises the combination of the data in thesource volume and the data to be overwritten by the updates transferredto the target volume.

With cascaded copy relationship, a source volume in one point-in-timecopy relationship, such as a FlashCopy®, may comprise target data ofanother copy relationship. A backward cascade copy relationshipcomprises a copy relationship whose target data is the source data in aforward copy relationship. There may be a chain of multiple backwardcascade copy relationships. If a request is directed to a track in avolume in one of the cascaded copy relationship, where the source andtarget volumes for each copy relationship are managed by differentservers, then the requested data may be located at any of the servers inthe cascaded copy relationships. A server receiving a request to a trackin a cascaded copy relationship may have to send messages to thedifferent servers in the cascaded copy relationships to determine wherethe data is located to retrieve.

There is a need in the art for improved techniques for managing cascadedcopy relationships.

SUMMARY

Provided are a computer program product, system, and method for using acascade flag to process a copy relationship having a backward cascadecopy relationship. Each of a plurality of copy relationships indicatesto copy source data to target data and has a cascade flag. The cascadeflag for a forward copy relationship of the copy relationships is set toa first value in response to determining that the source data for theforward copy relationship comprises target data for a backward copyrelationship and that a background copy operation specified to copysource data to target data of the backward copy relationship has notcompleted. The cascade flag for the forward copy relationship is set toa second value in response to determining that the backward copyrelationship does not have an uncompleted background copy operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a storage environment.

FIG. 2 illustrates an embodiment of components in a storage server.

FIG. 3 illustrates an embodiment of a copy relationship.

FIG. 4 illustrates an example of cascaded copy relationships establishedamong storage servers.

FIG. 5 illustrates an embodiment of operations to establish apoint-in-time copy relationship.

FIG. 6 illustrates an embodiment of operations to process a backgroundcopy operation that completes for a backward cascaded copy relationship.

FIG. 7 illustrates an embodiment of operations to process a request to adata unit in target data of a target copy relationship having a backwardcascaded copy relationship.

FIG. 8 illustrates a computing environment in which the components ofFIG. 1 may be implemented.

DETAILED DESCRIPTION

In a cascaded copy relationship, e.g., A to B, B to C, C to D, thetarget volume of one copy relationship comprises the source volume ofanother and each volume is at a different server, except for the volumesthat comprise both source and target data of different copyrelationship, which would be at the same server. Because of the cascadedrelationships, a forward copy relationship would not have the currentdata in the cascade if a backward copy relationship has not completedits background copy operation to copy the source data to the targetdata, which would then be propagated through the cascaded copyrelationships.

In such cascaded copy relationships, a copy manager in one serverprocessing a request to a data unit in one of the volumes in thecascaded copy relationships may need to read information from multipleof the servers in the cascade to determine the server in the cascade atwhich the current data is maintained including whether data has beencopied over from a backward cascade copy relationship to the source dataof the copy relationship being considered.

Described embodiments optimize cascaded copy relationship processing bymaintaining a cascade flag for each of the copy relationships toindicate whether there is a pending background copy operation for abackward copy relationship whose target data is the source data of thecopy relationship being considered. The use of the cascade flag wouldindicate in the current copy relationship whether the source data hasthe current data copied over from one or more prior backward copyrelationships. The use of the cascade flag avoids the need to messageone of the servers in the backward copy relationship to determinewhether a background copy operation completed and that that the sourcedata in the forward copy relationship would have current data.

Further, the cascade flag may be used to determine when to initiate abackground copy operation in one of the copy relationships in thecascade by only initiating the background copy operation after all thebackward cascade copy relationships have completed their background copyoperation to propagate the source data through the cascaded copyrelationships.

FIG. 1 illustrates an embodiment of a data storage environment having aplurality of servers 100 ₁, 100 ₂, 100 ₃ . . . 100 _(N) managing accessto volumes 102 ₁, 102 ₂, 102 ₃ . . . 102 _(N) of extents 104 ₁, 104 ₂,104 ₃ . . . 104 _(N) configured in storages 106 ₁, 106 ₂, 106 ₃ . . .106 _(N). Host systems 108 perform read and write operations withrespect to the volumes 102 ₁, 102 ₂, 102 ₃ . . . 102 _(N) over a network110. Extents 104 ₁, 104 ₂, 104 ₃ . . . 104 _(N) comprise groupings oftracks, blocks or other data units assigned to volumes 102 ₁, 102 ₂, 102₃ . . . 102 _(N).

The host 108 includes a copy manager program 112 _(H) to generaterequests to establish point-in-time copies of source data in one of thevolumes 102 ₁, 102 ₂, 102 ₃ . . . 102 _(N) to target data in another ofthe volumes 102 ₁, 102 ₂, 102 ₃ . . . 102 _(N) by submitting apoint-in-time copy establish request to the servers 100 ₁, 100 ₂, 100 ₃. . . 100 _(N). The point-in-time copies are defined in copyrelationships 300 maintained in the host 106 and servers 100 ₁, 100 ₂,100 ₃ . . . 100 _(N).

FIG. 2 shows the components included in each of the servers 100 ₁, 100₂, 100 ₃ . . . 100 _(N), including an operating system 114 andpoint-in-time copy managers 112 to create and manage point-in-timecopies, e.g., FlashCopy, snapshot, etc., in response to PiT copyestablish requests from the host system 108 copy manager 112 _(H) Whencreating a PiT copy, the server copy manager 112 generates copyrelationships 300 having information on the PiT copy created as of apoint-in-time. In one embodiment, when creating a point-in-time copyrelationship to copy data form a source volume 102 s, managed by asource server 100 _(S), to a target volume 102 _(T), managed by a targetserver 100 _(T), the source copy manager 112 _(S), in the source server100 _(S), and the target copy manager 112 _(T) in the target 100 _(T)server may each create source 300 _(S) and target 300 _(S) copyrelationships having information on the copy relationship between thesource 102 _(S) and target 102 _(T) volumes.

The operating system 114 in the servers 100 ₁, 100 ₂, 100 ₃ . . . 100_(N) assigns extents of tracks in the storage 106 ₁, 106 ₂, 106 ₃ . . .106 _(N) to the volumes 102 ₁, 102 ₂, 102 ₃ . . . 102 _(N), where datais stored in data units, such as tracks, logical block addresses (LBAs),extents, etc. An extent comprises a grouping of tracks, blocks or otherdata units that is assigned to volumes 102 ₁, 102 ₂, 102 ₃ . . . 102_(N). The operating system 114 maintain volume tables 116 providinginformation on the configured volumes 102 ₁, 102 ₂, 102 ₃ . . . 102_(N). The operating system 114 further manages I/O requests from thehost systems 108 with respect to the volumes 102 ₁, 102 ₂, 102 ₃ . . .102 _(N).

The storages 106 ₁, 106 ₂, 106 ₃ . . . 106 _(N) may comprise differenttypes or classes of storage devices, such as magnetic hard disk drives,solid state storage device (SSD) comprised of solid state electronics,EEPROM (Electrically Erasable Programmable Read-Only Memory), flashmemory, flash disk, Random Access Memory (RAM) drive, storage-classmemory (SCM), etc., Phase Change Memory (PCM), resistive random accessmemory (RRAM), spin transfer torque memory (STM-RAM), conductivebridging RAM (CBRAM), magnetic hard disk drive, optical disk, tape, etc.The volumes 102 _(S), 102 _(T) may further be configured from an arrayof devices, such as Just a Bunch of Disks (JBOD), Direct Access StorageDevice (DASD), Redundant Array of Independent Disks (RAID) array,virtualization device, etc. Further, the storages 106 ₁, 106 ₂, 106 ₃ .. . 106N may comprise heterogeneous storage devices from differentvendors and different types of storage devices, such as a first type ofstorage devices, e.g., hard disk drives, that have a slower datatransfer rate than a second type of storage devices, e.g., SSDs.

The network 110 may comprise a network such as one or moreinterconnected Local Area Networks (LAN), Storage Area Networks (SAN),Wide Area Network (WAN), peer-to-peer network, wireless network, etc.

FIG. 3 illustrates an instance of a copy relationship 300 _(i), such asa source and target copy relationship for a source and target pair in acopy relationship, which may include a PiT copy identifier 302identifying the copy relationship created by the source 112 _(S) andtarget 112 _(T) copy managers; a point-in-time 304 of the PiT copy 302,such that data is consistent as of that point-in-time 304; source data306, e.g., source volume 102 _(S), at a source server 100 _(S), fromwhich data is copied; target data 308, e.g., target volume 102 _(T), ata target server 100 _(T) to which the PiT data is copied; an extentrange 310 indicating an entire volume 102 _(S) or a range of extentsfrom a start track in a volume 102 _(S) comprising the source data inthe volume 102 _(S); change information 312, such as a change recordingbitmap, indicating whether each data unit (e.g., track) in the sourcedata 306 has or has not yet been copied to the target data 308; apersistence flag 314 indicating whether the copy relationship 300 _(i)is to be retained or persistent after a background copy operation forthe copy relationship 300 _(i) has completed; a cascade flag 316indicating whether there is a backward copy relationship 300 _(B) havingtarget data that is the source data 306 of the copy relationship 300_(i) that has a pending uncompleted background copy operation of thesource data to the target data; and a background copy flag 318indicating whether a background copy operation is to copy the sourcedata 306 to the target data 308 in the background. The background copyflag 318 is set to indicate no pending background copy operation aftercompleting a background copy operation or if there is no background copyoperation to perform.

FIG. 4 illustrates an example of backward and forward copy relationships300 _(i) in a cascade of copy relationships. Each copy relationship 300_(i) may have a source copy relationship 300 _(S,i) maintained at thesource server 100 _(S) managing the source volume 102 _(S) of therelationship 300 _(i) and a target copy relationship 300 _(T,i)maintained at the target server 100 _(T) managing the target volume 102_(T) of the relationship 300 _(i). For copy relationship 300 ₁, server100 ₁ maintains a source copy relationship 300 _(S,1) for copyrelationship 300 ₁ to copy source volume 102 ₁ to target volume 102 ₂,and server 100 ₂ has the target copy relationship 300 _(T,1) for copyrelationship 300 ₁. Since the volume 102 ₂ comprises a target volume ofcopy relationship 300 ₁ and a source volume for copy relationship 300 ₂,copy relationship 300 ₁ comprises a backward copy relationship to copyrelationship 300 ₂. For copy relationship 300 ₂, server 100 ₂ maintainsa source copy relationship 300 _(S,2) for copy relationship 300 ₂ tocopy source volume 102 ₂ to target volume 102 ₃, and server 100 ₃ hasthe target copy relationship 300 _(T,2) for copy relationship 300 ₂.Since the volume 102 ₃ comprises a target volume of copy relationship300 ₂ and a source volume for copy relationship 300 ₃, copy relationship300 ₂ comprises a backward copy relationship to copy relationship 300 ₃.For copy relationship 300 ₃, server 100 ₃ maintains a source copyrelationship 300 _(S,3) for copy relationship 300 ₃ to copy sourcevolume 102 ₃ to target volume 102 ₄, and server 100 ₄ has the targetcopy relationship 300 _(T,3) for copy relationship 300 ₃. Copyrelationships 300 ₂, 300 ₃, and 300 ₄ comprise forward copyrelationships to backward copy relationships 300 ₁, 300 ₂, and 300 ₃,respectively.

FIG. 5 illustrates an embodiment of operations performed by the copymanagers 112 in a source server 100 _(S) and target server 100 _(T) of acopy relationship 300 _(i). Upon receiving (at block 500), from the hostcopy manager 112 _(H), an establish request to establish a copyrelationship 300 _(i) for a range of extents in a source volume 102 _(S)to copy to a target volume 102 _(T), a server 100 _(S) executing a copymanager 112 creates (at block 502) source copy relationship 300 _(S,i),for new copy relationship 300 _(i), to indicate source data, e.g., asource volume 102 _(S), to copy to the target data, e.g., target volume102 _(T), in the establish copy request. The source copy manager 112determines whether the source data is also target data in a backwardcopy relationship 300 _(B). If so, then the source copy manager 112 _(S)determines (at block 506) whether the backward target copy relationship300 _(T,B) for the target data, e.g., target volume 102 _(T), indicatesin background copy field 318 whether a background operation is pendingor is not pending, such as completed. If there is a pending backgroundcopy operations, as indicated in background copy field 318, that has notcompleted, then the source copy manager 112 sets (at block 510) thecascade flag 316 for the source copy relationship 300 _(S,i) beingcreated to a first value indicating that the backward copy relationship300 _(B) has not completed its background copy operation.

If (from the no branch of block 504) there is no backward copyrelationship for the copy relationship being established or if (from theyes branch of block 506) a background copy relationship is indicated infield 318 as background completed or not specified, then the cascadeflag 316 for the source copy relationship 300 _(S,i) being establishedis set (at block 512) to a second value indicating there is no pendingbackground copy operation for the backward copy relationship 300 _(B) tocomplete.

After setting the cascade flag at block 510 or 512, a target copyrelationship 300 _(T,i) is created (at block 514), by the copy manager112 at the target server 100 _(T), indicating the source data 306 tocopy to the target data 308, and the cascade flag 316 for the targetcopy relationship 300 _(T) is set (at block 516) to the value set forthe cascade flag 316 in the source copy relationship 300 _(S) at block510 or 512. The server copy manager 112 _(S) may send a message to thetarget copy manager 112 _(T) to perform the operations at block 514 and516 for the target copy relationship 300 _(T) maintained for the targetvolume 102 _(T).

If (at block 518) there is a background copy operation specified for thecopy relationship to establish and the source cascade flag is set to thesecond value, indicating that there is no pending background copyoperation for the backward copy relationship to complete, then thesource copy manager 112 _(S) in the source server 100 s initiates (atblock 520) the background copy operation from the source data to thetarget data of the copy relationship being established. The source copymanager 112 _(S) in the source server 100 _(S) returns (at block 522)complete to the establish request after determining whether a backgroundcopy operation should be initiated for the copy relationship beingcreated.

With the described operations of FIG. 5, a background copy operation tocopy source data to target data for a copy relationship to establishwill not be initiated if a backward copy relationship has not completedits background copy operation. This insures that any updates to thesource data of the copy relationship to establish will be completed bythe backward copy relationship before the source data of the copyrelationship to establish is copied, to make sure the correct data isbeing transferred to the target data of the copy relationship beingestablished.

FIG. 6 illustrates an embodiment of operations performed by a copymanager 112 in a server 100 _(i) upon completing a background copyoperation from the source data 306 to the target data 308 and to resetthe cascade flag if the copy relationship 300 _(i) for which thebackground copy operation completed is a backward copy relationship to aforward copy relationship. Upon the background copy operation completing(at block 600) for a copy relationship 300 _(i), the copy manager 112,at the source server 100 _(S) of the copy relationship 300 _(i), updates(at block 602) the background copy flag 318 in the source copyrelationship 300 _(S,i), on the source server 100 _(S). The source copymanager 112 _(S) may send a message to the target copy manager 112 _(T)on the target server 100 _(T) to update the background copy flag 318 intarget copy relationship 300 _(T,i). If (at block 604) the persistenceflag 314 of the copy relationship 300 _(i) indicates that the copyrelationship 300 _(i) is not to be retained, then the source 300 _(S,i)and target 300 _(T,i) copy relationships are terminated (at block 606).The copy manager 112 on the source server 100 i would remove the sourcecopy relationship 300 _(S,i) and then send a message to the copy manager112 on the target server 100 _(j) to delete the target copy relationship300 _(T,i).

After processing the completing of the background copy operation, if (atblock 608) the target data 308 of the backward copy relationship 300_(B) is source data 306 of a forward copy relationship 300 _(F), thenthe cascade flags 316 in the source 300 _(S,F) and target 300 _(T,F)forward copy relationships are set (at block 610) to the second value,indicating that the background copy operation for the backward copyrelationship 300 _(B) completed. In one embodiment, the target copymanager 112 in the target server 100 _(T,B), of the backward copyrelationship, upon receiving a message from the source copy manager 112in the source server 100 _(S,B) of the backward copy relationship 300_(B), may send a message to the source server 100 _(S,F) of the forwardcopy relationship 300 _(F) to update the cascade flag 316 in the sourcecopy relationship 300 _(S,F), and the copy manager 112 in the sourceserver 100 _(S,F) may send a message to the target server 100 _(T,F) ofthe forward copy relationship 300 _(F) to update the cascade flag 316 inthe target copy relationship 300 _(T,F) of the forward copy relationship300 _(F).

Upon updating the cascade flag 316 (at block 610), the copy manager 112in the source server 100 _(S,F) of the forward copy relationship 300_(F) determines (at block 612) whether there is a background copyoperation, as indicated in field 318, specified for the forward copyrelationship 300 _(F) in the source copy relationship 300 _(S,F). If (atblock 612) a background copy operation is specified, then the copymanager 112 on the source server 100 _(S,F) of the forward copyrelationship 300 _(F) initiates (at block 614) the background copyoperation to the target data 308, e.g., target volume 102 ₁, in thetarget server 102 ₁. Upon the background copy operation completing (atblock 616), the background copy operation field 318 in the source 300_(S,F) and target 300 _(T,F) copy relationships is indicated ascompleted (at block 618). In one embodiment, the copy manager 112 in thesource server 100 _(S,F) may update the background copy flag 318 in thesource copy relationship 300 _(S,F) of the forward copy relationship 300_(F) upon completing the background copy operation and then send amessage the copy manager 112 in the target server 100 _(T,F) to updatethe target copy relationship 300 _(T,F) of the forward copy relationship300 _(F) to update its background copy flag 318. Completing thebackground copy operation on the forward copy relationship 300 _(F)would trigger the target server 100 _(T,F) copy manager to start theoperations at block 600 to process the background copy operation anddetermine if there are any further forward copy relationships havingsource data comprising the target data of the forward copy relationship300 _(F) for which the background copy operation completed.

The operations of FIG. 6 provide operations for the copy managers in theservers having the source and target copy relationships to updatecascade flags to indicate that a background copy operation for abackward copy relation completed, which then allows the forward copyrelationship to complete its background copy operation. This ensuresthat when a background copy operation is performed for a copy operationhaving a backward copy relationship, all the data from the backward copyrelationships are available at the source data for the background copyoperation of the forward copy relationship.

FIG. 7 illustrates an embodiment of operations performed by a copymanager 112 in a target server 100 _(i) to process a request for a dataunit, e.g., track, in target data, e.g., a target volume 102 _(i), of atarget copy relationship 300 _(T,i). Upon receiving (at block 700) therequest for the requested data unit, a current level target copyrelationship is set (at block 702) to the target copy relationship 300_(T,i) having the target data to which the request is directed. If (atblock 704) the current level target copy relationship change information312 indicates that the source data was copied over to the requested dataunit in the target storage 308, then the requested data is returned (atblock 706) from the target data for the current level copy relationship.If (at block 704) the change information 312 for the current leveltarget copy relationship indicates that the source data has not yet beencopied to the target data for the requested data unit, then adetermination is made if (at block 708) the cascade flag 316 set for thecurrent level target copy relationship is set to the first value,indicating a backward cascade copy relationship to the current leveltarget copy relationship has not completed its background copyoperation. If (at block 708) the cascade flag 316 indicates that thebackward copy relationship does not have an uncompleted background copyoperation (e.g., the second value), then the requested data is returned(at block 710) from the source data 306 for the current level targetcopy relationship.

In one embodiment, the copy manager 112 in the target server 100 _(i)that received the request may directly read the requested data from thetarget or source volume at blocks 706 and 710 upon determining thecurrent data for the requested data unit is at the target data or sourcedata. By returning requested data directly from the source data for acurrent level target relationship, the copy manager 112 on the targetserver 100 _(i) avoids having to send messages to the source server 100_(j) to inquire about the status of the source data, but instead maydirectly read the source data from the backward copy relationship.

If (at block 708) the backward copy relationship has a pendinguncompleted background copy operation to perform (e.g., the firstvalue), a determination is made (at block 712) of a backward target copyrelationship having target data comprising the source data 306 of thecurrent level target copy relationship and sets (at block 714) thecurrent level target copy relationship to the determined target copyrelationship of the backward copy relationship to determine whether thecurrent data for the requested data unit is available at the backwardcopy relationship.

In certain embodiments, the copy manager 112 in the target server 100_(i) that received the request may send message to the source server ofthe current level target copy relationship to determine whether there isa backward target copy relationship at the source server for the sourcedata. This allows one copy manager 112 to either query servers todetermine whether they have a backward cascade relationship to furtherconsider or directly access the data unit from a source or target volumein the backward copy relationship in the cascade.

The operations of FIG. 7 optimize the determination of the location ofthe data by using a cascade flag 316 to determine whether the data ofthe requested data unit is located in a backward copy relationship thathas not yet completed its background copy operation, and then based onthat determination locate the data for the requested data unit in thesource or target data of the backward copy relationship or a furtherdown level backward copy relationship.

In certain embodiments, each source and target data may comprise asource volume and target volume on different storages managed bydifferent servers, where each server maintains source and/or target copyrelationship information to manage the copy relationships. In suchembodiments messages need to be sent to a server at which source ortarget copy relationship information is maintained for volumes managedby the server to perform operations with respect to the copyrelationships. In alternative embodiments, source and target copyrelationships and source and target volumes for one copy relationshipmay be maintained at one server, as opposed to separate servers.

The reference characters used herein, such as i, j, N are used to denotea variable number of instances of an element, which may represent thesame or different values, and may represent the same or different valuewhen used with different or the same elements in different describedinstances.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Java, Smalltalk, C++ or the like,and conventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The computational components of FIG. 1, including the host 108 and theservers 100 ₁, 100 ₂, 100 ₃ . . . 100 _(N) may be implemented in one ormore computer systems, such as the computer system 802 shown in FIG. 8.Computer system/server 802 may be described in the general context ofcomputer system executable instructions, such as program modules, beingexecuted by a computer system. Generally, program modules may includeroutines, programs, objects, components, logic, data structures, and soon that perform particular tasks or implement particular abstract datatypes. Computer system/server 802 may be practiced in distributed cloudcomputing environments where tasks are performed by remote processingdevices that are linked through a communications network. In adistributed cloud computing environment, program modules may be locatedin both local and remote computer system storage media including memorystorage devices.

As shown in FIG. 8, the computer system/server 802 is shown in the formof a general-purpose computing device. The components of computersystem/server 802 may include, but are not limited to, one or moreprocessors or processing units 804, a system memory 806, and a bus 808that couples various system components including system memory 806 toprocessor 804. Bus 808 represents one or more of any of several types ofbus structures, including a memory bus or memory controller, aperipheral bus, an accelerated graphics port, and a processor or localbus using any of a variety of bus architectures. By way of example, andnot limitation, such architectures include Industry StandardArchitecture (ISA) bus, Micro Channel Architecture (MCA) bus, EnhancedISA (EISA) bus, Video Electronics Standards Association (VESA) localbus, and Peripheral Component Interconnects (PCI) bus.

Computer system/server 802 typically includes a variety of computersystem readable media. Such media may be any available media that isaccessible by computer system/server 802, and it includes both volatileand non-volatile media, removable and non-removable media.

System memory 806 can include computer system readable media in the formof volatile memory, such as random access memory (RAM) 810 and/or cachememory 812. Computer system/server 802 may further include otherremovable/non-removable, volatile/non-volatile computer system storagemedia. By way of example only, storage system 813 can be provided forreading from and writing to a non-removable, non-volatile magnetic media(not shown and typically called a “hard drive”). Although not shown, amagnetic disk drive for reading from and writing to a removable,non-volatile magnetic disk (e.g., a “floppy disk”), and an optical diskdrive for reading from or writing to a removable, non-volatile opticaldisk such as a CD-ROM, DVD-ROM or other optical media can be provided.In such instances, each can be connected to bus 808 by one or more datamedia interfaces. As will be further depicted and described below,memory 806 may include at least one program product having a set (e.g.,at least one) of program modules that are configured to carry out thefunctions of embodiments of the invention.

Program/utility 814, having a set (at least one) of program modules 816,may be stored in memory 806 by way of example, and not limitation, aswell as an operating system, one or more application programs, otherprogram modules, and program data. Each of the operating system, one ormore application programs, other program modules, and program data orsome combination thereof, may include an implementation of a networkingenvironment. The components of the computer 802 may be implemented asprogram modules 816 which generally carry out the functions and/ormethodologies of embodiments of the invention as described herein. Thesystems of FIG. 1 may be implemented in one or more computer systems802, where if they are implemented in multiple computer systems 802,then the computer systems may communicate over a network.

Computer system/server 802 may also communicate with one or moreexternal devices 818 such as a keyboard, a pointing device, a display820, etc.; one or more devices that enable a user to interact withcomputer system/server 802; and/or any devices (e.g., network card,modem, etc.) that enable computer system/server 802 to communicate withone or more other computing devices. Such communication can occur viaInput/Output (I/O) interfaces 822. Still yet, computer system/server 802can communicate with one or more networks such as a local area network(LAN), a general wide area network (WAN), and/or a public network (e.g.,the Internet) via network adapter 824. As depicted, network adapter 824communicates with the other components of computer system/server 802 viabus 808. It should be understood that although not shown, other hardwareand/or software components could be used in conjunction with computersystem/server 802. Examples, include, but are not limited to: microcode,device drivers, redundant processing units, external disk drive arrays,RAID systems, tape drives, and data archival storage systems, etc.

The terms “an embodiment”, “embodiment”, “embodiments”, “theembodiment”, “the embodiments”, “one or more embodiments”, “someembodiments”, and “one embodiment” mean “one or more (but not all)embodiments of the present invention(s)” unless expressly specifiedotherwise.

The terms “including”, “comprising”, “having” and variations thereofmean “including but not limited to”, unless expressly specifiedotherwise.

The enumerated listing of items does not imply that any or all of theitems are mutually exclusive, unless expressly specified otherwise.

The terms “a”, “an” and “the” mean “one or more”, unless expresslyspecified otherwise.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries.

A description of an embodiment with several components in communicationwith each other does not imply that all such components are required. Onthe contrary a variety of optional components are described toillustrate the wide variety of possible embodiments of the presentinvention.

When a single device or article is described herein, it will be readilyapparent that more than one device/article (whether or not theycooperate) may be used in place of a single device/article. Similarly,where more than one device or article is described herein (whether ornot they cooperate), it will be readily apparent that a singledevice/article may be used in place of the more than one device orarticle or a different number of devices/articles may be used instead ofthe shown number of devices or programs. The functionality and/or thefeatures of a device may be alternatively embodied by one or more otherdevices which are not explicitly described as having suchfunctionality/features. Thus, other embodiments of the present inventionneed not include the device itself.

The foregoing description of various embodiments of the invention hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed. Many modifications and variations are possible in lightof the above teaching. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto. The above specification, examples and data provide acomplete description of the manufacture and use of the composition ofthe invention. Since many embodiments of the invention can be madewithout departing from the spirit and scope of the invention, theinvention resides in the claims herein after appended.

What is claimed is:
 1. A computer program product for managing copyrelationships of data in at least one storage, wherein the computerprogram product comprises a computer readable storage medium havingprogram instructions embodied therewith, the program instructionsexecutable by a processor to cause operations, the operationscomprising: creating and maintaining information for a source copyrelationship in a source server, where the source copy relationshipindicates source data to copy to target data and the source servermanages access to the source data in the at least one storage; andsetting a cascade flag in the information for the source copyrelationship when the source data comprises target data of a backwardcopy relationship to indicate whether the source data has current datafrom the backward copy relationship.
 2. The computer program product ofclaim 1, wherein the operations further comprise: creating andmaintaining information for a target copy relationship in a targetserver, where the target data indicates the source data to copy to thetarget data also in the source copy relationship and the target servermanages access to the target data in the at least one storage; andsetting a cascade flag in the information for the target copyrelationship to a value for the cascade flag in the source copyrelationship.
 3. The computer program product of claim 1, wherein theoperations further comprise: initiating a background copy operation tocopy the source data to the target data in the source copy relationshipin response to the cascade flag of the source copy relationshipindicating the source data has the current data from the backward copyrelationship.
 4. The computer program product of claim 1, wherein thesource data has the current data from the backward copy relationshipwhen the backward copy relationship has completed a background copy ofsource data to target data in the backward copy relationship.
 5. Thecomputer program product of claim 1, wherein the operations furthercomprise: completing a background copy operation to copy source data ofthe backward copy relationship to the target data of the backward copyrelationship; determining whether target data of the completedbackground copy operation comprises source data of a forward copyrelationship; and setting a cascade flag of the forward copyrelationship in the information for the source copy relationship toindicate that the source data for the forward copy relationship iscurrent in response to determining that the target data of the completedbackground copy operation comprises source data of the forward copyrelationship.
 6. The computer program product of claim 5, wherein theoperations further comprise: in response to the setting of the cascadeflag of the forward copy relationship in the information for the sourcecopy relationship to indicate that the source data for the forward copyrelationship is current, determining whether there is a background copyoperation to perform for the forward copy relationship; and initiatingthe background copy operation to perform for the forward copyrelationship to copy the source data for the forward copy relationshipto the target data for the forward copy relationship in response todetermining that there is the background copy operation to perform forthe forward copy relationship.
 7. The computer program product of claim1, wherein the operations further comprise: receiving a request to adata unit in the target data of the source copy relationship; inresponse to the source data for the source copy relationship having datafor the data unit to copy to the target data and the cascade flagindicating that the source data for the copy source relationship doesnot comprise current data, determining a background copy relationshiphaving target data comprising the source data of the source copyrelationship; and accessing current data for the data unit from thedetermined background copy relationship for the request to the dataunit.
 8. A system for managing copy relationships of data in at leastone storage, comprising: a source server manages access to source datain the at least one storage comprising: a first processor; and a firstcomputer readable storage medium having program instructions executed bythe first processor to cause operations, the operations comprising:creating and maintaining information for a source copy relationship toindicate source data to copy to target data; and setting a cascade flagin the information for the source copy relationship when the source datacomprises target data of a backward copy relationship to indicatewhether the source data has current data from the backward copyrelationship.
 9. The system of claim 8, comprising: a target server thatmanages access to target data in the at least one storage comprising: asecond processor; and a second computer readable storage medium havingprogram instructions executed by the second processor to causeoperations, the operations comprising: creating and maintaininginformation for a target copy relationship to indicate the source datato copy to the target data also in the source copy relationship; andsetting a cascade flag in information for the target copy relationshipto a value for the cascade flag in the source copy relationship.
 10. Thesystem of claim 8, wherein the operations further comprise: initiating abackground copy operation to copy the source data to the target data inthe source copy relationship in response to the cascade flag indicatingthe source data has the current data from the backward copyrelationship.
 11. The system of claim 8, wherein the source data has thecurrent data from the backward copy relationship when the backward copyrelationship has completed a background copy of source data to targetdata in the backward copy relationship.
 12. The system of claim 8,wherein the operations further comprise: completing a background copyoperation to copy source data of the backward copy relationship to thetarget data of the backward copy relationship; determining whethertarget data of the completed background copy operation comprises sourcedata of a forward copy relationship; and setting a cascade flag of theforward copy relationship in the information for the source copyrelationship to indicate that the source data for the forward copyrelationship is current in response to determining that the target dataof the completed background copy operation comprises source data of theforward copy relationship.
 13. The system of claim 12, wherein theoperations further comprise: in response to the setting of the cascadeflag of the forward copy relationship in the information for the sourcecopy relationship to indicate that the source data for the forward copyrelationship is current, determining whether there is a background copyoperation to perform for the forward copy relationship; and initiatingthe background copy operation to perform for the forward copyrelationship to copy the source data for the forward copy relationshipto the target data for the forward copy relationship in response todetermining that there is the background copy operation to perform forthe forward copy relationship.
 14. The system of claim 8, wherein theoperations further comprise: receiving a request to a data unit in thetarget data of the source copy relationship; in response to the sourcedata for the source copy relationship having data for the data unit tocopy to the target data and the cascade flag of the source copyrelationship indicating that the source data for the source copyrelationship does not comprise current data, determining a backgroundcopy relationship having target data comprising the source data of thesource copy relationship; and accessing current data for the data unitfrom the determined background copy relationship for the request to thedata unit.
 15. A method for managing copy relationships of data in atleast one storage, comprising: creating and maintaining information fora source copy relationship a source server that indicates source data tocopy to target data where the source server manages access to the sourcedata in the at least one storage; and setting a cascade flag in theinformation for the source copy relationship when the source datacomprises target data of a backward copy relationship to indicatewhether the source data has current data from the backward copyrelationship.
 16. The method of claim 15, further comprising: creatingand maintaining information for a target copy relationship in a targetserver, where the target copy relationship indicates the source data tocopy to the target data also in the source copy relationship and thetarget server manages access to the target data in the at least onestorage; and setting a cascade flag in the information for the targetcopy relationship to a value for the cascade flag in the source copyrelationship.
 17. The method of claim 15, further comprising: initiatinga background copy operation to copy the source data to the target datain the source copy relationship in response to the cascade flag in theinformation for source copy relationship indicating the source data hasthe current data from the backward copy relationship.
 18. The method ofclaim 15, wherein the source data has the current data from the backwardcopy relationship when the backward copy relationship has completed abackground copy of source data to target data in the backward copyrelationship.
 19. The method of claim 15, further comprising: completinga background copy operation to copy source data of the backward copyrelationship to the target data of the backward copy relationship;determining whether target data of the completed background copyoperation comprises source data of a forward copy relationship; andsetting a cascade flag of the forward copy relationship in theinformation for the source copy relationship to indicate that the sourcedata for the forward copy relationship is current in response todetermining that the target data of the completed background copyoperation comprises source data of the forward copy relationship. 20.The method of claim 19, further comprising: in response to the settingof the cascade flag of the forward copy relationship in the informationfor the source copy relationship to indicate that the source data forthe forward copy relationship is current, determining whether there is abackground copy operation to perform for the forward copy relationship;and initiating the background copy operation to perform for the forwardcopy relationship to copy the source data for the forward copyrelationship to the target data for the forward copy relationship inresponse to determining that there is the background copy operation toperform for the forward copy relationship.
 21. The method of claim 15,further comprising: receiving a request to a data unit in the targetdata of the source copy relationship; in response to the source data forthe source copy relationship having data for the data unit to copy tothe target data and the cascade flag indicating that the source data forthe source copy relationship does not comprise current data, determininga background copy relationship having target data comprising the sourcedata of the source copy relationship; and accessing current data for thedata unit from the determined background copy relationship for therequest to the data unit.